I agree that there's nothing fraudulent with using a tool you would use on the job when you are interviewing. But in no way are LLMs equivalent to calculators. Calculators actually give the correct answer reliably, unlike LLMs. A sporadically reliable tool is worse than no tool at all.
LLMs have come a long way. If you give gpt-o3-mini the same interview question five times, chances are good that it will get it right all five times. Yes, it's not a calculator, but it's approaching one.